# The largest prime number ever has just been discovered

A recently discovered prime number, which goes by M77233917, has been found to comprise 23,249,425 digits, making it the largest prime ever.

The number is something of a marvel; it’s the 50th Mersenne prime number ever discovered, which are found in the deceptively simple way of multiplying twos together a bunch, and then subtracting one from the final number. M77232917 (not really household name material) was found by multiplying 77,323,917 twos and subtracting one.

The discovery blows the previous record – a Mersenne prime uncovered in January 2016 – out the water by adding nearly a million digits (910,807, to be exact) to the number. It’s no mean feat, either; as numbers increase, prime numbers (those divisible by one and themselves) becoming increasingly hard to come by. Their distribution in the cumulative succession of numbers is irregular, meaning there’s no pattern to foresee what the subsequent prime will be. Algorithms, for all their myriad purposes, are all but useless in this domain.

The discovery was made by Tennessee local, 51-year-old Jonathan Pace, an electrical engineer who’s devoted 14 years of his life to hunting prime numbers. Mr Pace made the discovery by running specialised software on his PC while competing in the Great Internet Mersenne Prime Search (GIMPS). He is set to receive \$3,000 (£2,200) for the monumental find.

The discovery isn’t actually a 2018 one – found on Boxing Day 2017, it took six days of computing to prove its prime status, a feat succeeded by four different software programs running on four different hardware configurations to test the find.

Long prime numbers are useful in encryption, given that they’re so difficult to find, with many users combining two prime numbers to make a fairly robust encryption key. However, as computers become more sophisticated, the prime numbers in question need to become longer and longer in order to keep up – although the 50th Mersenne prime is so lengthy as to actually preclude it from this purpose.

Pace’s discovery is so large that it would take 9,000 pages if printed out, or come in at 118 kilometres at 2 digits per centimetre. Download M77232917 here at your peril.

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